Demethylation of aromatic hydrocarbons



ULT/MHTE YIELD IVE/6H7 PER CENT Sept. 3, 1957 H. L. COONRADT ETAL2,305,267

DEMETHYLATION OF AROMATIC HYDROCARBONS Filed Sept. 16, 1952 550 900 050moo 1050 mm TEMPERflTl/RE 0 E NVENTO United States Patent Ofifice2,805,267 Patented Sept. 3, 1957 DEMETHYLATION F AROMATIC HYDROCARBONSHarry L. Coonradt and Charles J. Plank, Woodbury, and Barton W. Rope,Mullica Hill, N. L, assignors to Socony Mobil Oil Company, Inc., acorporation of New York Application September 16, 1952, Serial No.309,927

6 Claims. (Cl. 260-672) This invention relates to the demethylation ofmethylsubstituted organic compounds. It is more particularly concernedwith the catalytic removal of one or more methyl groups frommethyl-substituted aromatic hydrocarbons, in the presence of a novelcatalyst.

Dealkylation of alkylaromatic compounds has been effected in excellentyields, by many processes well known in the art. As those familiar withthe art will appreciate, however, demethylation, as distinguished fromdealkylation, has been more difficult of achievement. In order to effectthe removal of one or more methyl groups from a methyl-substitutedaromatic compound, conditions must be used which diflfer considerablyfrom those used in dealkylation. For example, in U. 8. Patent No.2,194,- 449, to Sachanen et al., it has been proposed to demethylatemethylnaphthalenes to naphthalene in the presence of a clay typecatalyst, at temperatures of between about 800 F. and about 1200 F.,temperatures of about 900 F. being preferred. It is significant to note,however, that dealkylation reactions proceed to almost 100 percent yieldof dealkylated products. On the other hand, even under the optimumconditions known in the prior art, demcthylation reactions have effectedmuch lower yields of demethylated product, i. e., in the neighborhood ofaround about 55 percent yield.

It has now been found that methyl-substituted aromatic compounds can bedemethylated in superior yields, by a process which is simple andcommercially feasible. It has been discovered that the removal of one ormore methyl groups from a methyl-substituted aromatic hydrocarbon can beeffected by contacting the same with a novel catalyst comprising a thinsilica-alumina shell overlaying a silica base.

Accordingly, it is an object of the present invention to provide acommercially feasible process for dcmethylating methyl-substitutedaromatic compounds. Another object is to provide a process for achievingthe demethylation of methyl-substituted aromatic hydrocarbons insuperior yields. A further object is to provide a new catalytic processfor demethylating methyl-substituted aromatic hydrocarbons. A specificobject is to provide a process for effecting the removal of one or moremethyl groups from a methylnaphthalene, in the presence of a novelcatalyst. A more specific object is to provide a process for producingnaphthalene from methylnaphthalenes in superior yields by contacting themethylnaphthalenes with a catalyst comprising a thin silica-aluminashell overlaying a silica base. Other objects and advantages of thepresent invention will become apparent to those skilled in the art, fromthe following detailed description.

The present invention provides a process for demethylating amethyl-substituted aromatic compound, which comprises contacting themethyl-substituted aromatic compound with a catalyst comprising a thinsilica-a1umina shell overlaying a silica core, at a temperature ofbetween about 900 F. and about 1200 F., and for a period of time ofbetween about one second and about three minutes.

The process of this invention is generally applicable to thedemethylation of any methyl-substituted aromatic hydrocarbon, includingmonomethyl-substituted aromatic hydrocarbons and polymethyl-substitutedaromatic hydrocarbons. In the case of the latter compounds, one or moremethyl groups can be removed. Thus, for example, a xylene can bedernethylated to produce benzene or toluene, dependent upon the extentof demethylation desired. The present process is also applicable tocharge stocks containing methyl-substituted aromatic hydrocarbons inadmixture with other hydrocarbons, such as highly-aromatic petroleumfractions and the like, as well as to relatively pure methyl-substitutedaromatic hydrocarbons. Non-limiting examples of the charge stocks whichcan be demethylated by the present process are toluene, o-xylene,p-xylene, trimethylbenzenes, a-methylnaphthalene, fl-methylnaphthalene,guaiene, 1,4-dimethylnaphthalene, a-methylanthracene,2,4-dimethylanthracene, 3-methylphenanthrene, and the like; and mixturesthereof.

The catalyst utilized herein is fully described in a copendingapplication, Serial Number 256,389, filed November 14, 1951, by CharlesJ. Plank, now Patent No. 2,746,936, one of the inventors herein.Reference should be made thereto for further details. The base orcarrier material for the catalyst is a porous silica gel. This carriercan be in the form of granules of any desired size and shape ordinarilyused for catalytic materials. A convenient carrier consists of sphericalbead-like particles of silica gel. Such particles can be prepared by anyfeasible procedure, such as the method described in U. S. Patent No.2,384,964.

In order to prepare the catalyst used in the process of this invention,the pores of the carrier are first partially filled with a liquid whichis chemically unreactive with the silica gel. Suitable liquids arewater; liquids having a viscosity of at least about 20 centipoises, asdescribed in U. S. Patent No. 2,456,578; and water-miscible organicliquids set forth in U. S. Patent No. 2,456,577. Nonlimiting examples ofthe liquids are aromatic hydrocarbons, such as, benzene, toluene,xylene, etc.; halogenated organic compounds, such as, carbontetrachloride, chlorobenzenes, etc.; alcohols, such as methanol,ethanol, pentanol, glycol, gylcerine, etc.; ketones, such as, acetone,methylethyl ketone, etc.; aldehydes, such as, acetaldehyde, etc.;ethers, such as, ethyl ether, etc.; nitrated compounds, such as,nitrobenzene; heterocyclic compounds, such as, furan, thiophene, etc.;and derivatives thereof.

It is to be noted that the pore-filling operation is purely a physicalone. The liquids do not react, chemically, with the silica gel. Thepartial filling of the pores can be accomplished by several methods. Thecarrier can be immersed in the liquid for a period of time which islimited so as to effect partial filling. Alternatively, knowing the poresize and the amount of carrier, a measured amount of liquid justsufiicient to effect the desired partial filling of the pores can beused. By another method, the carrier can be completely saturated withthe liquid, and subsequently subjected to vacuum, so as to remove partof the liquid. If undried silica gel is used, it can be subjected tovacuum to effect the same result of partial pore filling, without firstdrying the wet silica gel. The extent to which the pores are filled, ofcourse, will depend upon the desired depth of the surface coating orshell, as will become apparent hereinafter.

After the pores of the silica gel are partially filled, the silica gelis impregnated with a solution of an aluminum salt capable of beingconverted to alumina by calcination. If desired, the impregnated carriercan be further treated with a basic solution, such as, NH4OH or NaOHsolutions, to precipitate aluminum hydroxide in the surface pores. Thesolvent for the aluminum salt can be the same liquid used for partiallyfilling the pores or it can be different therefrom. In fact, the degreeof miscibility of the two liquids is determinative of the next step inpreparing the catalyst.

As will be recognized, the unfinished catalyst, at this point, consistsof a silica gel carrier having the inner portion of its pores filledwith an inert liquid, and having the outer, or surface, portions of itspores filled with a solution of an aluminum salt or with a suspension ofaluminum hydroxide.

The wet, impregnated catalyst is then dried, at temperatures of about200-500 F., to remove the solvents and liquids used to partially fillthe pores. When the solvent for the aluminum salt and the filling liquidare substantially immiscible, drying need not be rapid. If, however, thetwo liquids are miscible, or the same liquids (which is often the case),drying should be effected as quickly as possible. Otherwise, thealuminum salt may migrate or diffuse towards the center of the carrier,thus destroying the desired concentration of aluminum salt near thesurface of the carrier. The dried catalyst is then calcined, suitably attemperatures of between about 800 F. and about 1400 F.

The finished catalyst, produced as described briefly herein and in moredetail in the Plank application, supra, consists of a center or core ofsilica covered with a thin layer or shell of silica-alumina. Thethickness of this shell will depend upon the depth of impregnation. Inother words, it depends upon the amount of the pore volume which is notfilled with liquid during the initial step in preparing the catalyst. Inthe interests of brevity, this catalyst is hereinafter referred to as anegg-shell catalyst, so-called because of the resemblance of the catalystshell to the shell of an egg. The egg-shell catalyst herein described isto be distinguished from the coprecipitated alumina-silica catalysts andfrom the silica catalysts which have been impregnated with alumina tothe full depth of the pores.

The process of this invention is effected by contacting themethyl-substituted aromatic compound charge material with theaforedescribed egg-shell catalyst, at elevated temperatures, for arelatively short period of time, in any vessel suitable for carrying outcatalytic reactions, and having provision for heat input to maintaincatalyst temperature. The process, of course, can be performed in abatch process. Preferably, however, a continuous operation is used. Insuch an operation, the charge is passed through the reactor in contactwith the catalyst. Then the reaction product is subjected to a productseparation operation. The portion of the charge stock which remainsundemethylated and/or which is incompletely demethylated (as withpolymethyl charge materials) can be recycled to the reactor, until themaximum ultimate conversion has been effected.

The temperature of the egg-shell catalyst is maintained at between about900 F. and about 1200 F., preferably, betwecn about 950 F. and about1050 F. The contact time is dependent upon the temperature and upon thenature of the reactants. In general, the contact time varies inverselywith the temperature, and beween about one second and about threeminutes.

The present process can be carried out at any pressure, subatmospheric,atmospheric, or superatmospheric. At elevated temperatures andpressures, however, coking becomes more pronounced. Accordingly, it ispreferred to operate under atmospheric pressure, or at pressuresslightly below atmospheric pressure. Advantageous results can beobtained when hydrogen gas is added to the reaction vessel. It isdesirable to use hydrogen under pressure. Accordingly, superatmospheriopressures are most advantageous when operating in the presence of addedhydrogen gas.

The following examples are for the purpose of demonstrating the processof the present invention and the superiority thereof. It must bestrictly understood that this invention is not to be limited by thereactants and conditions used in the examples, or by the operations andmanipulations involved therein. As will be apparent to those skilled inthe art, other reactants and conditions, as set forth hereinbefore, canbe used to practice this invention.

APPARATUS AND OPERATION The reactor used in the runs described in theexamples was a stainless steel tube suspended in a bath of molten lead.The temperature of the lead was controlled to maintain the catalysttemperature constant to within about 10 F. Catalyst temperature wasmeasured by means of thermocouples extending into the top, middle, andbottom portions of the catalyst bed. A total volume of about cubiccentimeters of catalyst was placed in the reactor. Accessory equipmentincluded a heated, thermostatically controlled burette for measuring thecharge, pumps, preheater coils, a condensing and collecting system foraromatic and gaseous products, and a system for determining the amountof coke on the catalyst by a combustion method.

In operation, the catalyst, at operating temperature, was purged withnitrogen gas; followed by a flushing with hydrogen when used in the run.Then, the charge material, in the liquid state, together with addedgases or liquids, was passed through a preheater to raise thetemperature thereof to the reaction temperature. The combined charge wasthen passed downwardly through the catalyst bed at a rate sufficient toeffect the desired contact time. A sample of the total gas collected wasanalyzed in the mass spectrometer to determine its composition and theweight of the components. The principal component was methane.

The amount of coke laid down on the catalyst was determined bycombustion methods, i. e., by converting it to carbon dioxide andanalyzing therefor. The aromatic products were distilled on a columnhaving 15 theoretical plates. The amounts of the aromatic hydrocarbonsin the product were determined by (1) fractionation, or (2) byultraviolet absorption analysis.

RUNS USING SiO2-Al2O3 CRACKING CATALYST Examples 1 through 13 Example 14A portion of bead cracking catalyst, as used in the preceding examples,was steam treated. This treatment lowered the activity index of thecatalyst from about 42 to about 35. A run was made using this catalystand Z-methylnaphthalene. Pertinent data and results therefor are setforth in Table I. In Table II are summarized the average data forconversion from methylnaphthalene to naphthalene under variousconditions, as more fully set forth in Table I.

Yield of Products, Weight Percent Yield of Products Ulti- Charge stock 5Length Methyl- Contact Pcr Pass mate Weight Percent Example Temp., ofRun, naphtha- Time,

F. Min. lene L. Sec.

H. 6. VJ Nephtha- Resi- Coke Gas Total Naphtha- Coke Gas G. G./Min. lencdue lene 48. 6 1. 97 950 24. 6 0. 803 10. 1 9. 1 79. 9 6. 0. 8 95. 7 57.2 37. 8 5. 0 48. 4 2.0 950 24. 2 0. 812 10.0 7. 9 82. 4 6. 6 0.8 97. 751. 7 43.1 5. 2 48. 4 2.0 950 24. 2 0. 810 10. 0 10. 7 76. 2 7. 0 0.894.8 57. 8 37. 9 4. 3 48. 1.93 l. 000 25.1 0. 785 10.0 15. 5 72. 7 8. 31.2 97.6 G2. 0 33. 2 4. 8 48. 3 1.92 1, 000 25. 2 0. 779 10.2 14. l 73.3 7. 7 1. 4 96. 5 60. 8 33. 2 6. 0 48. 4 1. 93 1,000 25.1 0.784 10.0 16.3 71. 5 9.5 1. 2 98. 5 60. 4 35. 2 4.4 43. 4 1. 92 1, 000 25. 2 0. 77910. 1 14. 5 70. 9 8. 9 1. 4 95. 7 58. 5 35.9 5. 0 99.0 1.93 1, 00B 51. 30. 800 10.0 13.0 75. 3 6. 8 1. 4 96. 5 61. 3 32. 0 6. 7 98. 6 1.93 1,000 51.1 0. 784 10.0 11.8 79.0 7.0 1. 3 99. 7 58. 7 34. 8 6.5 48. 4 1.80 1, 100 26. 8 0. 732 10. (l 21. 5 58. 3 14. 2 3. l 97. 1 55. 3 36. 78.0 48. 5 1.81 1,100 26. 8 0.735 9. 9 23. 5 53. 8 15.9 3.1 96. 3 55. 337. 4 7.3 48. 7 1.81 1, 100 26. 7 0. 735 10.0 20. [l 57. 2 l5. 5 1. 494. 2 54. 2 42.0 3. 8 98. 2 1. 79 1,100 54. 9 O. 725 10.1 19.0 61. 712.9 3. 2 96. 8 54.1 36. 8 9.1 98. 6 1. 93 1, 000 51. 2 0. 780 10.0 10.l 7.8 1.0 53. 5 41. 2 5. 3

I Bead cracking catalyst oi 42 A.I.iresl1 dried (10.1 wt. percent A1103)unless otherwise stated. Volume of catalyst-160 cc. 52-mcthylnaphthalone-Ultraviolet absorption analysis indicated 99.4%purity.

' 2-methylnaphthaleneEastInan practical.

6 Volume 2'rnethylnaphthalene charge at 50 C./vol. catalyst/hour. Basedon total charge to reactor and assuming 150 cc. of voids.

I Based on ratios of naphthalene, coke and gas.

I Bead cracking catalyst steam treated to 35.3 AI.

TABLE II.DEMETHYLATION 0F METHYLNAPH'IHA- LENE l SILICA-ALUMINA BEADCATALYST, YIELD OF NAPHTHALENE e Average values from experiments undersimilar conditions as listed in Table I.

Examples 16 and 17 Two runs were made in which Z-mcthylnaphthalene wascharged to the reactor containing the egg-shell catalyst described inExample 15, at 1000 F. catalyst temperature. In each run, all conditionswere maintained identical, in order to demonstrate the reproducibilityof results. Pertinent data and results for these runs are set forth inTable III.

Examples 18 and 19 Runs were made, using the same reactant and catalystas in Examples 16 and 17, except that the temperatures employed were1100 F. and 900 F., respectively. Pertinent data and results thereforare set forth in Table III.

TABLE III.-DEMETHYLATION OF METHYLNAPHTHALENE EGG-SHELL CATALYST 8 Yieldof Products Weight Percent Yield of Products Ulti- Charge Stock b LengthMethyl- Contact Per Pass matc Weight Percent Example Temp, of Run,naphtha- Time,

F. Min. lene L. Sec

H.S.V. Nnphthir Rcsi- Coke Gus Total Nnphtha- Coke Gas G. (IL/Min. loneduo lene 98. 6 1. 93 1, 000 51. 2 0. 781 10. D 8. 8 85. 4 4.1 0.4 98. 766. 4 30. 5 3. 1 98. 7 1. 93 1, 000 51. 2 0. 782 10.0 8. 2 8B. 3 4. 2 0.4 99. 1 64. 3 32. 5 3. 2 98. 6 1. 79 1,100 55. 0 0. 727 10.0 14. 7 74. 29. 0 1. 3 99. 2 58. 7 38. 0 5. 3 98. 6 2. 075 900 47. 5 0. 842 10. O 2,5 95. 4 2. 6 0. l 100. [i 48. 1 50. D 1. 9

4 Egg-shell catalyst, 31.6 Al.

b 2-methylnaphthalene-Reilly (purified; ultraviolet analysis indicated99.4% purity).

v Volume of Z-mcthylnaphtholcnc at G./vol. catalyst/hour. Based on totalcharge to reactor and assuming 150 cc. of voids.

' Based on ratios of naphthalene, coke and gas.

RUNS USING THE EGG-SHELL CATALYST Example 1 5 A catalyst was preparedfrom silica hydrogel beads produced by the method described in U. S.Patent No. 2,384,946, at a pH of 7.0. Three and one half liters of thesilica hydrogel were aged for 15 hours at 42-50 F. Then, the hydrogclbeads were treated with sulfuric acid and subsequently washed free ofsulfate ion. The wet, washed beads were impregnated with aluminumnitrate by immersing them, for fifteen minutes, in a 10 percent aqueoussolution of aluminum nitrate nonahydrate. Thereafter, the beads weredried overnight at about 280 F., and then calcined overnight at 1000" F.The catalyst, thus prepared, consisted essentially of a shell ofalumina-silica over a core of silica. It had a bulk density of 0.80 andan activity index of about 32.

0 of the process of the preent invention.

The foregoing examples demonstrate the superiority It is recognized thatthe yield per pass using the egg-shell catalyst is somewhat less thanwhen the silica-alumina cracking catalyst is used. Due to less cokingand gaseous degradation products, however, the ultimate yields aremarkedly higher, when using the egg-shell catalyst. This superiority ismore remarkable when it is borne in mind that the catalyst activityindex of the silica-alumina catalyst used in Examples 1 through 13 wasgreater than that of the egg-shell catalyst used in Examples 16 through18.

In the figure attached hereto, the curves compare graphically therelationship between the ultimate yield of naphthalene frommcthylnaphthalene and catalyst tempcraturc, for each catalyst; otherconditions remaining constant. The curves are based upon the data setforth in Tables I, I1, and III, for runs made in the same reactor for acontact time of about 10 seconds. It will be noted that the maximumultimate yield obtained with the eggshell catalyst of 32 activity index(Curve A), under optimum conditions, was about 66 percent, based on theweight of methylnaphthalene charged. The maximum ultimate yield obtainedwith the silica-alumina catalyst (Curve B) was about 61 weight percent,using the more active catalyst of 42 activity index. Using asilicaalumina catalyst of lower activity index (Example 14), which ismore comparable to that of the egg-shell catalyst. the maximum yield wasabout 54 weight percent (Point Thus, it will be apparent that undersimilar conditions of contact time, temperature, and catalyst activityindex, the process of the present invention effects almost percentgreater yield than was obtained with the silicaalumina catalyst.

The products produced by the process of this invention have many useswell known to those skilled in the art. Thus, benzene is used as asolvent and as an intermediate for preparing chlorinated benzeneinsecticides, phenol, etc. Many halo compounds, cresols, and benzylcompounds are produced from toluene. Naphthalene is a well knownlarvicide, and an intermediate for the production of phthalic anhydrideby oxidation thereof. Methylphthalic anhydrides are produced frommethylnaphthalenes.

Although the present invention has been described with preferredembodiments, it is to be understood that modifications and variationscan be resorted to without departing from the spirit and scope of thisinvention, as those skilled in the art will readily understand. Suchvariations and modifications are considered to be within the scope andpurview of the appended claims.

What is claimed is:

1. A process for demethylating a methyl-substituted aromatic compound,which comprises contacting the methyl-substituted aromatic compound witha catalyst comprising a thin silica-alumina shell overlaying a silicacore, at a temperature of between about 900 F. and about 1200 F, and fora period of time of between about one second and about three minutes;said catalyst being produced by partially filling the pores of a poroussilica gel with a liquid which is chemically unrcactive with said silicagel, impregnating said silica gel having the pores thereof thuspartially filled, with an aqueous solution of an aluminum salt, dryingthe thusimpregnated silica gel and calcining the dried, impregnatedsilica gel.

2. A process for demethylating a monomethyl-substituted aromatichydrocarbon, which comprises contacting said aromatic hydrocarbon with acatalyst comprising a thin silica-alumina shell overlaying a silicacore, at a temperature of between about 900 F. and about 1200 F., andfor a period of time of between about one second and about threeminutes; said catalyst being produced by partially filling the pores ofa porous silica gel with a liquid which is chemically unreactive withsaid silica gel, impregnating said silica gel having the pores thereofthus partially filled, with an aqueous solution of an aluminum salt,drying the thus-impregnated silica gel and calcining the dried,impregnated silica gel.

3. A method for producing naphthalene from a methylnaphthalene, whichcomprises contacting said methylnaphthalene with a catalyst comprising athin silicaalumina shell overlaying a silica core, at a temperature ofbetween about 900 F. and about 1200 F., and for a period of time ofbetween about one second and about three minutes; said catalyst beingproduced by partially filling the pores of a porous silica gel with aliquid which is chemically unreactive with said silica gel, impregnatingsaid silica gel having the pores thereof thus partially filled, with anaqueous solution of an aluminum salt, drying the thus-impregnated silicagel and calcining the dried, impregnated silica gel.

4. A continuous process for producing naphthalene from amethylnaphthalene, which comprises contacting said methylnaphthalenewith a catalyst comprising a thin silica-alumina shell overlaying asilica core, at a temperature of between about 950 F. and about 1050 F.,for a period of time of between about one second and about threeminutes; separating the naphthalene from undeicthylatedmethylnaphthalene; and recycling said undemcthylated methylnaphthalene;said catalyst being produced by partially filling the pores of a poroussilica gel with a liquid which is chemically unreactive with said silicagel, impregnating said silica gel having the pores thereof thuspartially filled, with an aqueous solution of an aluminum salt, dryingthe thus-impregnated silica gel and calcining the dried, impregnatedsilica gel.

5. A process for producing naphthalene from 2-methylnaphthalene, whichcomprises contacting said Z-methylnaphthalene with a catalyst comprisinga thin silicaalurnina shell overlaying a silica core, at a temperatureof between about 950 F. and about 1050 F., and for a period of time ofbetween about one second and about three minutes; said catalyst beingproduced by partially filling the pores of a porous silica gel with aliquid which is chemically unreactive with said silica gel, impregnatingsaid silica gel having the pores thereof thus partially filled, with anaqueous solution of an aluminum salt, drying the thus-impregnated silicagel and calcining the dried, impregnated silica gel.

6. A process for producing naphthalene from 2-methylnaphthalene, whichcomprises contacting said 2-methylnaphthalene with a catalyst comprisinga thin silica-alumina shell overlaying a silica core, at a temperatureof about 1000 F., and for about ten seconds; said catalyst beingproduced by partially filling the pores of a porous silica gel with aliquid which is chemically unreactive with said silica gel, impregnatingsaid silica gel having the pores thereof thus partially filled, with anaqueous solution of an aluminum salt, drying the thus-impregnated silicagel and calcining the dried, impregnated silica gel.

References Cited in the file of this patent UNITED STATES PATENTS2,194,449 Sachanen et al. Mar. 19, 1940 2,211,208 Ipatiefi et al Aug.13, 1940 2,280,649 Kanhofer Apr. 21, 1942 2,380,279 Welty July 10, 19452,384,942 Marisic Sept. 18, 1945 2,606,159 Owen Aug. 5, 1952 2,746,936Plank May 22, 1956 2,750,432 Coonradt et al June 12, 1956 OTHERREFERENCES Thomas: J. A. C. 5., vol. 66, pages 1694-6 (1944). Sachanen:Conversion of Petroleum, 2nd edition, page 88, published by ReinholdPub. Cor., New York, N. Y. (1948).

1. A PROCESS FOR DEMETHYLATING A METHYL-SUBSTITUTED AROMATIC COMPOUND,WHICH COMPRISES CONTACTING THE METHYL-SUBSTITUTED AROMATIC COMPOUND WITHA CATALYST COMPRISING A THIN SILICA-ALUMINA SHELL OVERLAYING A SILICACORE, AT A TEMPERATURE OF BETWEEN ABOUT 900*F. AND ABOUT 1200*F., ANDFOR A PERIOD OF TIME BETWEEN ABOUT ONE SECOND AND ABOUT THREE MINUTES;SAID CATALYST BEING PRODUCED BY PARTIALLY FILLING THE PORES OF A POROUSSILICA GEL WITH A LIQUID WHICH IS CHEMICALLY UNREACTIVE WITH SAID SILICAGEL, IMPREGNATING SAID SILICA GEL HAVING THE PORES THEREOF THUSPARTIALLY FILLED, WITH AN AQUEOUS SOLUTION OF AN ALUMINUM SALT, DRYINGTHE THUS-IMPREGNATED SILICA GEL AND CALCINING THE DRIED, IMPREGNATEDSILICA GEL.